Gas discharge tube with phosphor coating and elongate electrodes

ABSTRACT

A gas discharge tube is provided which comprises a glass tube, a coating of phosphor applied to the inner walls of the glass tube, a pair of electrodes disposed in parallel to each other along the substantial length of the glass tube, and some amounts of mercury and a neon-argon gas mixture or a neon-helium-argon gas mixture.

United States Patent 1191 3,814,969 June 4, 1974 Kamiya et a1.

Oct.25, 1971 GAS DISCHARGE TUBE WITH PHOSPHOR COATING AND ELONGATE ELECTRODES Inventors: Shigeru Kamiya; Hitoshi Ohtsuka;

Kensaku Ueda, all of Osaka; Masashi Sangen, Kobe, all of Japan Assignee: Matsushita Electronics Corporation,

Osaka-fu, Japan Filed: Oct. 24, 1972 Appl. No.: 299,909

Foreign Application Priority Data Japanm, 46-84833 Oct. 25, 1971 Japan 46-84834 u,s. c|. .....313 4s6, 313/217, 3'13/226', 313/490 int: Cl H0lj 61/06, H01j 61/64 Field of Search 313/109, 217, 218, 225, 313/226 Primary Examiner-Palmer C. Demeo [57] ABSTRACT A gas discharge tube is provided which comprises a glass tube, acoating of phosphor applied to the inner walls of the glass tube, a pair of electrodes disposed in parallel to each other along the substantial length of the glass tube, and some amounts of mercury and a neon-argon gas mixture or a neon-helium-argon gas mixture.

6 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION The present invention relates to generally a glow lamp and more particularly an improvement of a glow lamp of the type consisting of a pair of parallel electrodes and inert gases sealed into a glass tube whereby the phosphor coating applied to the inner walls of the glass tube may emit the light of a desired color by the mercury glow discharge.

Glow lamps of the type comprising a glass tube and, a pair of parallel electrodes sealed in a neon atmosphere contained within the glass tube have been widely used as indicator lights because they may be readily operated by connecting them to the electrical supply circuit through a ballast resistor and the reduced power consumption does not result in a corresponding reduction of brightness. The neon glow lamps have been also widely used because the glow discharge is readily produced in the sealed neon gas, and neon glow lamps in various shapes are available. However the neon glow lamp generally can emit only one color ranging in wavelength from 650 to 750 nanometers.

In the glow lamp of the type in which the ultra-violet rays emitted by the mercury glow discharge causes the phosphor to emit the light in visible range, argon is generally sealed into a glass tube containing also some amount of mercury. In the glow lamp of the type described, the brightness of light in the visible range emitted from argon gas is extremely weak so that only the light emitted from the phosphor is perceived by the eyes. However, the mobility of mercury ions in argon gas is so small that when the length of a pair of electrodes sealed in the glass tube is long the light emission along the whole length of the electrodes becomes extremely difficult. As a result, the electrodes of the glow lamp of the type described are inevitably limited to a shorter length. It is of course possible to produce the light along the whole length of the electrodes even when they are long when the glow lamp is coupled in series through a low-resistance resistor to a power source. In this case, the surface load of the electrodes is increased so that blackening of the inner walls of the glass tube due tothe vaporization of the electrodes occurs, resulting in the decrease in brightness of emitted light. This presents a serious problem in practice.

SUMMARY OF THE INVENTION One of the objects of the present invention is therefore to overcome the defects and problems encountered in the prior art glow lamps.

Another object of the present invention is to provide a glow lamp which may emit the light along the whole length of the electrodes thereof with a high luminous efficiency when operated at a practical current.

More particularly, another object of the present invention is to provide the composition of gases sealed into a glass tube which may uniformly produce the light along the whole length of a pair of electrodes longer than 30 millimeters in length disposed in parallel to each other in the glass tube of a glow tube of the type having the coating of phosphor applied to the inner walls thereof, the glow lamp being operated at a normal current.

In order to accomplish the above and other objects of the present invention, the inventor made extensive studies and experiments and found out that the gas mixture sealed into glass tube preferably consists of 5 percent by volume of a neon and 95 60 percent by volume of argon or neon-helium-argon gas mixture with helium being less than one half by volume of neon in addition to some amount of mercury.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING:

The single FIGURE is a schematic sectional view of a gas discharge tube in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

In the single FIGURE, a glass tube I has an inner diameter ranging from four to 15 millimeters and a length depending upon that of a pair of electrodes 3 and 4 which are disposed in parallel with and spaced apart from each other by a predetermined distance within the glass tube 1. The inner wall of the glass tube 1 is covered with a coating 2 of phosphor, and the pair of electrodes 3 and 4 are supported by insulating blocks 5 and 6 respectively and are connected at one ends to lead wires 9 and 10, respectively, which extend air-tightly through one end or base 7 of the glass tube I. The glass tube 1 contains some amounts of mercury 8 and the argon-neon gas containing 5 30 percent by volume of neon or neon-helium-argon gas mixture containing 5 30 percent by volume of neon and helium less than one half by volume of neon.

' When the glass tube 1 has an inner diameter less than 4 millimeters, the diameter of electrodes becomes too small so that the surface load becomes too great, thus resulting in blackening of the inner walls within a considerably short service life. On the other hand when the glass tube 1 has an inner diameter greater than 15 milli- ,meters, the distance from the electrodes to the phosphor coating becomes too great so that sufficient brightness cannot be attained.

The pair of electrodes 3 and 4 may be conventional ones made of nickel, nickel alloy or nickel-plated steel wires. The spacing between the pair of electrodes 3 and 4 is determined depending upon a voltage impressed between them and is for example of the order of 0.7 millimeters when the voltage is 200 220 volts. In this case, the discharge starting voltage is about volts at room temperature.

The length of a pair of electrodes is dependent upon the purpose of use and determines the composition of gases sealed into the glass tube. The insulating blocks 5 and 6 are used to hold the pair of electrodes'3 and 4 in parallel so that they may not contact to each other even under vibrations, and are made of ceramics such as steatite or mica. It is not necessary to support both ends of the pair of electrodes by the insulating blocks, and only one end of the pair of electrodes may be supported by the insulating blocks if so desired.

The gas discharge tube in accordance with the present invention may also use any phosphor used in conventional fluorescent lamps, and the phosphors which may be excited to emit the light of a narrow spectrum such as divalent europium activated phosphate alkaline earth metals, divalent manganese activated zinc silicate, trivalent'europium activated yttrium vanadate, trivalent dysprosium activated yttrium vanadate, tetravalent manganese activated magnesium arsenate and tetravalent manganese activated magnesium germafluoride are especially effective when used in the gas discharge lamps which are used as indicator lamps. In some special cases, the phosphors which may be excited to emit the ultra-violet rays may be coated to a glass tube which may transmit the ultra-violet rays.

The amount of mercury sealed into the glass tube is not so critical, but it is preferable that the amount of mercury is not much greater than that which would just saturate the lamp when it is turned on, in order to avoid the short-circuiting the pair of electrodes.

The composition of gases sealed into the glass tube is one of the fundamental conditions for attaining the uniform light emission of the glow lamp type with the construction described above. The composition of gases must be selected depending upon the length of electrodes, and it is necessary to seal some amounts of gases to improve the mobility of mercury ions in order to attain the uniform glow discharge throughout the whole length of electrodes. The latter condition is especially important when the length of electrodes becomes longer.

The uniformity of mercury glow discharge around the electrodes as well as the mercuryand neon-glows were extensively investigated by the inventors by varying the ratio of neon to argon. It was found out that when the ratio of neon is in excess of 30 percent, red light excited by the neon glow discharge becomes stronger while light emitted from the phosphor which is excited by the mercury glow discharge becomes weak so that the colors of the light emitted by the phosphor and by the neon glow discharge are mixed. When the length of electrodes is within 100 millimeters, the gas mixture consisting of 30 percent of neon and 70 percent of argon may produce a desired lamp color. When the length of the electrodes is short and is for example 30 millimeters, the ratio of neon may be decreased. Especially when the ratio of neon is less than 5 percent the lamp color is not substantially different from that of a gas discharge tube containing only argon. Therefore the lower limit of the ratio of neon is considered 5 percent.

When the length of the electrodes is in excess of I00 millimeters, the gas mixture consisting of 30 percent of neon and 70 percent of argon is not sufficient to improve the mobility of mercury ions, so that the light cannot be produced uniformly along the whole length of the electrodes. Helium may be also used to improve the mobility of mercury ions, but the brightness of helium emission spectrum in the visible region is so weak that helium is sealed in a glow discharge tube containing the long electrodes so as to produce the light along the whole length of the electrodes. However, the inventors found out that the use of the gas mixture consisting of helium and argon will cause considerable damages to the electrodes. The inventors made extensive studies and experiments in order to find out the suitable ratio among neon, argon and helium which may overcome the above described defect. It was found out that when the amount of helium is less than one half of that of neon the damages to the electrodes may be considerably reduced. The gas mixture consisting of neon, argon and helium in fact serves to reduce the current load which is required to produce the uniform glow discharge along the whole length of the electrodes. For example, in case of the electrodes having a length of 120 millimeters and the gas mixture consisting of argon and 30 percent of neon, the current load of 1.5 mA per 10 millimeters is required to produce the uniform glow discharge along the whole length of the electrodes, but in case of the gas mixture consisting of 30 percent of neon, 10 percent of helium and 60 percent of argon, the uniform glow discharge may be produced by the current load of only 0.8 mA per 10 mm of electrode. in the former case, blackening of the inner walls of the glass tube takes place within a very short time, but in the latter case blackening is not observed even after a long service time.

The composition of the gas mixture consisting of neon, helium and argon may be selected in various manners. For example the gas mixture consisting of 30 percent of neon and percent of argon or 25 percent of neon, 5 percent of helium and 70 percent of argon may be used when the length of the electrodes is of the order of millimeters. The composition of the gas mixture consisting of neon, helium and argon will not cause a great difference in light produced as far as the amount of helium is less than one half of that of neon.

In order to specifically point out the novel features of the gas discharge tube in accordance with the present invention, one example thereof will be described hereinafter. 4

EXAMPLE 1 The coating of divalent europium activated strontium pyrophosphate was applied to the inner wall of the glass tube of 7 mm in inner diameter and mm in length, the phosphor used being the blue light emission phosphor with the peak wavelength of 4.200 A.

The pair of manganese-nickel alloy electrodes of l millimeter in diameter and 80 mm in length were disposed in parallel with and spaced apart from each other by 0.7 mm in the glass tube which contained 8 mg of mercury and the gas mixture consisting of 25 percent by volume of neon and 75 percent of argon at a pressure of 40 mmHg.

The pair of electrodes were firmly inserted into the holes of the blocks made of steatite capable of withstanding the heat up to 1,200C. In order to degas the electrodes they were heated in the inert gas atmosphere at about 800C.

The gas discharge tube was turned on at the voltage of 200 AC volts and the current of 10 mA. Blue light emission was normal and the desired spectrum energy distribution was attained.

When the gas mixture consisting of 35 percent of neon and 65 percent of argon was sealed into a glass tube similar in construction to the above described glass tube, blue light emission was adversely affected by red light produced by the neon glow discharge so that the desired lamp color was not obtained.

When the phosphor coating of manganese activated zine silicate was applied, the lamp color was green. When the phosphor coating of europium activated yttrium vanadate was applied, the lamp color was red. When the phosphor coatings were magnesium germafluoride and dysprosium activated yttrium vanadate, the lamp colors were deep red and yellow, respectively.

EXAMPLE 2 The phosphor coating of divalent europium activated strontium pyrophosphate was applied to the inner wall of a glass tube of mm in inner diameter and 160 mm in length. The phosphor is a blue-light-emission phosphor with the peak wavelength of 4,200 A. A pair of manganese-nickel alloy electrodes one millimeter in diameter and 140 mm in length were disposed in the glass tube in parallel with and spaced apart from each other by 0.7 mm,'and the gas mixture consisting of 26 percent of neon, 8 percent of helium and 66 percent of argon and the amount of l5 mg of mercury were sealed in the glass tube under the pressure of 40 mmHg. The pair of electrodes were firmly inserted into the holes of the blocks made from steatite capable of withstanding the heat up to l,200C, and were degased in the inert gas atmosphere at about 800C.

The gas discharge tube thus obtained was turned on atthe AC voltage of 200 volts and a current of 10 mA. Blue light emission was normal and the desired spectrum distribution was obtained without causing the damages to the electrodes.

When the gas mixture consisting of 35 percent by volume of neon, 10 percent of helium and 55 percent of argon was sealed, blue light emission was adversely affected by red light produced by the neon glow discharge. When the gas mixture consisting of 25 percent by volume of neon, percent of helium and 65 per cent of argon was sealed, the lamp color was blue, but the electrodes were so damaged that the service life was very short.

When the various phosphor coatings same as those a. an air-tight glass tube,

b. a coating of phosphor applied to the inner wall of said glass tube,

- c. a pair of electrodes longer than '30 millimeters in length disposed in parallel to each other extending in the axial direction of said glass tube, and

d. a filling in said glass tube consisting of mercury and an inert gas mixture consisting of 5-30 percent neon, helium in an amount less than one half of said neon, and the remainder argon.

2. A gas discharge tube as defined in claim 1 wherein said coating of phosphor consists of one of divalent europium activated phosphate alkaline earth metals, divalent manganese activated zinc silicate, trivalent europium activated yttrium vanadate, trivalent dysprosium activated yttrium vanadate, tetravalent manganese activated magnesium arsenate and tetravalent manganese activated magnesium germafluoride.

3. A gas discharge tube as defined in claim 1 wherein said sealed inert gases consist of 30 percent of neon and percent of argon.

4. A gas discharge tube as defined in claim 3 wherein said coating of phosphor consists of one of divalent europium activated phosphate alkaline earth metals, divalent manganese activated zinc silicate, trivalent europium activated yttrium vanadate, trivalent dysprosium activated yttrium vanadate, tetravalent manganese activated magnesium arsenate and tetravalent manganese activated magnesium germafluoride.

5. A gas discharge lamp as defined in claim 1 wherein said sealed inert gases consist of 26 percent of neon, 8 percent of helium and 66 percent of argon.

6. A gas discharge tube as defined in claim 5 wherein said coating of phosphor consists of one of divalent europium activated phosphate alkaline. earth metals, divalent manganese activated zinc silicate, trivalent europium activated yttrium vanadate, trivalent dysprosium activated yttrium vanadate, tetravalent manganese activated magnesium arsenate and tetravalent manganese activated magnesium germafluoride. 

2. A gas discharge tube as defined in claim 1 wherein said coating of phosphor consists of one of divalent europium activated phosphate alkaline earth metals, divalent manganese activated zinc silicate, trivalent europium activated yttrium vanadate, trivalent dysprosium activated yttrium vanadate, tetravalent manganese activated magnesium arsenate and tetravalent manganese activated magnesium germafluoride.
 3. A gas discharge tube as defined in claim 1 wherein said sealed inert gases consist of 30 percent of neon and 70 percent of argon.
 4. A gas discharge tube as defined in claim 3 wherein said coating of phosphor consists of one of divalent europium activated phosphate alkaline earth metals, divalent manganese activated zinc silicate, trivalent europium activated yttrium vanadate, trivalent dysprosium activated yttrium vanadate, tetravalent manganese activated magnesium arsenate and tetravalent manganese activated magnesium germafluoride.
 5. A gas discharge lamp as defined in claim 1 wherein said sealed inert gases consist of 26 percent of neon, 8 percent of helium and 66 percent of argon.
 6. A gas discharge tube as defined in claim 5 wherein said coating of phosphor consists of one of divalent europium activated phosphate alkaline earth metals, divalent manganese activated zinc silicate, trivalent europium activated yttrium vanadate, trivalent dysprosium activated yttrium vanadate, tetravalent manganese activated magnesium arsenate and tetravalent manganese activated magnesium germafluoride. 